The invention relates to a method of and a device for tuning a resonant circuit. This method and this device can be used in television, and more specifically to adjust the tuning of the "cloche" circuit of a television receiver of the SECAM type.
To adjust such a circuit during the manufacture of the television set, several methods can be used.
It is, for example, possible to use a system which measures the current entering the resonant circuit and the voltage at its terminals, and the adjustment is correct when these two values are in phase at the nominal frequency. The phase is compared on the screen of an oscilloscope and the adjustment is effected manually. Using an automatic adjustment would be difficult as the very accurate phase difference measurement is not simple.
It is alternatively possible to use, to determine the adjustment to be performed so as to tune the resonant circuit, a signal which is produced by a frequency discriminator coupled to an output of the resonant circuit, and to excite the resonant circuit repeatedly and sequentially in two different modes. A method of this type is disclosed in the document DE-A 2,702,565, which teaches the observation on the screen of an oscilloscope of the signal supplied by the discriminator while the resonant circuit is sequentially excited by frequencies located symmetrically with respect to the nominal frequency of the "cloche" circuit, with the object of manually adjusting the resonant circuit.